Several common PHP algorithm interview questions

function king($m, $n) {
	if (1 >= $n) {
		return $n;
	}
	$monkeys = range(1, $n);
	$count = $n;
	while ($count > 1) {
		$remainder = $m % $count;
		unset($monkeys[$remainder - 1]);
		$monkeys = array_values($monkeys);
		$count--;
	}
	return array_shift($monkeys);
}

function cows ($n) {
	$cows = [1];
	for ($i = 1; $i <= $n; $i++) {
		// 新出生的牛
		$new_number = 0;
		foreach ($cows as $age => $num) {
			// 4岁到14岁的牛生育新的母牛
			if ($age >= 3 &
			&
			$age <
			= 13) {
				$new_number += $num;
			}
		}
		// 将新出生的牛加到数组开头
		array_unshift($cows, $new_number);
		// 取出数组的前20个单元
		$cows = array_slice($cows, 0, 20);
	}
	return array_sum($cows);
}

function bubble_sort ($array) {
	$array = array_values($array);
	for ($i = 0; $i < count($array); $i++) {
		for ($j = 0;$j < count($array) - $i - 1; $j++) {
			if ($array[$j] > $array[$j + 1]) {
				$temp = $array[$j + 1];
				$array[$j + 1] = $array[$j];
				$array[$j] = $temp;
			}
		}
	}
	return $array;
}

function quick_sort ($array) {
	if (count($array) <
	= 1) {
		return $array;
	}
	$left_array = [];
	$right_array = [];
	$key = array_shift($array);
	foreach ($array as $value) {
		if ($key > $value) {
			$left_array[] = $value;
		} else {
			$right_array[] = $value;
		}
	}
	return array_merge(quick_sort($left_array), [$key], quick_sort($right_array));
}

function select_sort ($array) {
	$sort_array = [];
	while (count($array)) {
		$min = null;
		$min_key = null;
		foreach ($array as $key => $value) {
			if (is_null($min)) {
				$min = $value;
				$min_key = $key;
			} elseif ($min > $value) {
				$min = $value;
				$min_key = $key;
			}
		}
		$sort_array[] = $min;
		unset($array[$min_key]);
	}
	return $sort_array;
}

function unique_char ($str) {
	$arr = array_unique(str_split($str));
	sort($arr);
	return implode('', $arr);
}

function all_file ($dir) {
	if (is_dir($dir)) {
		$resource = opendir($dir);
		while ($file = readdir($resource)) {
			if (in_array($file, ['.', '..'])) {
				continue;
			} elseif (is_dir($dir . '/' . $file)) {
				all_file($dir . '/' . $file);
			} else {
				echo $dir . '/' . $file, "\n";
			}
		}
	} else {
		echo $dir, "\n";
	}
}

function ladder($steps) {
	return $steps <
	2 ? 1 : ladder($steps - 1) + ladder($steps - 2);
}

class Node {
	public $value;
	public $left;
	public $right;
}
/**
 * 先序遍历 根节点 ---> 左子树 ---> 右子树
 *
 * @param $root
 */
function preorder ($root) {
	echo $root->value;
	if (!empty($root->left)) {
		preorder($root->left);
	}
	if (!empty($root->right)) {
		preorder($root->right);
	}
}
/**
 * 中序遍历，左子树---> 根节点 ---> 右子树
 *
 * @param $root
 */
function inorder ($root) {
	if (!empty($root->left)) {
		inorder($root->left);
	}
	echo $root->value;
	if (!empty($root->right)) {
		inorder($root->right);
	}
}
/**
 * 后序遍历，左子树 ---> 右子树 ---> 根节点
 *
 * @param $root
 */
function tailorder ($root) {
	if (!empty($root->left)) {
		tailorder($root->left);
	}
	if (!empty($root->right)) {
		tailorder($root->right);
	}
	echo $root->value;
}
$d = new Node;
$d->value = 'D';
$b = new Node;
$b->value = 'B';
$b->left = $d;
$e = new Node;
$e->value = 'E';
$f = new Node;
$f->value = 'F';
$c = new Node;
$c->value = 'C';
$c->left = $e;
$c->right = $f;
$a = new Node;
$a->value = 'A';
$a->left = $b;
$a->right = $c;
preorder($a);
echo "\n";
inorder($a);
echo "\n";
tailorder($a);
echo "\n";